1. Field of the Invention
The present invention relates to an image sensor and a focal point detection device utilized in an autofocus camera or the like and a camera with the image sensor and the focal point detection device.
2. Description of Related Art
There are autofocus cameras that adjust the focal point of the photographic lens by detecting a subject image present in a focal point detection area set within the photographic image plane. Such an autofocus camera often adopts the so-called phase difference detection method. The focal point adjustment is achieved as described below through the phase difference detection method.
A pair of subject images is formed with light fluxes having entered through the photographic lens and passed through a focal point detection area set within the photographic image plane by using a focal point detection optical system which is provided as a separate unit independent of the photographic optical system constituted with the photographic lens. Electrical charges the quantities of which correspond to the levels of the light intensity of the pair of subject images are stored at a light receiving unit constituted with a pair of photoelectric conversion element arrays and are then converted to electrical signals corresponding to the quantities of stored electrical charges. During this process, the length of time over which the electrical charges are stored is controlled so as to output the converted electrical signals (subject image signals) with the optimal intensity.
Based upon the extent to which the image positions of the subject images according to the contrasts of the subject image signals thus obtained (hereafter simply referred to as “contrast”) at the individual photoelectric conversion element arrays constituting the light receiving unit are offset relative to each other, the defocus quantity indicating the extent of defocusing of the photographic optical system relative to the predicted focal plane is calculated. By driving the focusing lens in correspondence to the calculated defocus quantity, a focus match is achieved for the photographic optical system.
A focal point detection device known in the related art, which is used in an autofocus camera adopting the phase difference detection method described above, sets a plurality of focal point detection areas within the photographic image plane and individually controls the lengths of storage time for a plurality of light receiving units each provided in correspondence to one of the focal point detection areas (see U.S. Pat. No. 5,418,594).